1. Field of the Invention
The present invention relates to a tandem rotation detector capable of effectively preventing the occurrence of leakage flux between rotation angle detection mechanisms so that high-precision detection can be always realized.
2. Description of the Prior Art
FIG. 1 shows a sectional side view of a conventional tandem rotation detector.
As shown in FIG. 1, this type of tandem rotation detector (for example, Japanese Patent Application Laid-Open No. 2003-098019) is used to detect the rotation angles of rotary shafts. The rotation detector has a rotary shaft 104A and a rotary shaft 104B arranged in series in a central portion of a cylindrical housing 101. A first rotation angle detection mechanism 102A for detecting the rotation angle of the rotary shaft 104A, and a second rotation angle detection mechanism 102B for detecting the rotation angle of the rotary shaft 104B are arranged inside the housing 101. In the first rotation angle detection mechanism 102A, a first outer core 110A and a first stator core 130A are arranged in parallel on the inner surface of the housing 101. A first inner core 120A is mounted on the rotary shaft 104A so as to face the first outer core 110A, and a first rotor core 140A is mounted on the rotary shaft 104A so as to face the first stator core 130A.
A coil 111A is wound on the first outer core 110A with the terminals connected to two outer core pins 112A placed side by side in the horizontal direction, respectively, through which an AC voltage is applied. A coil 121A is wound on the first inner core 120A.
Coils 131A are wound on a plurality of annular stator core teeth 133A provided around the first stator core 130A. The coils 131A have four terminals connected to each other in the X direction (horizontal direction) and the Y direction (vertical direction) respectively, and the four terminals of the coils 131A are connected to four stator core pins 132A which are placed side by side in the horizontal direction, respectively. Coils 141A are wound on a plurality of rotor core teeth 142A provided on the circumference of the rotary shaft 104A.
In such a structure, when an AC voltage is applied to the coil 111A of the first outer core 110A, a voltage corresponding to the rotation angle of the rotary shaft 104A is induced into the first stator core 130A through the first inner core 120A and the first rotor core 140A in the first rotation angle detection mechanism 102A, thereby detecting the rotation angle of the rotary shaft 104A.
Like the first rotation angle detection mechanism 102A, the second rotation angle detection mechanism 102B includes a second outer core 110B, a second inner core 120B, a second stator core 130B, and a second rotor core 140B to detect the rotation angle of the rotary shaft 104B. Then, based on the detected rotation angles of the rotary shafts 104A and 104B, a difference between both rotation angles is detected. Numeral 112B designates outer core pins to which the terminals of coils of the second outer core 110B are connected, while numeral 132B designates four stator core pins to which the respective terminals of coils of the second stator core 130B are connected.
The conventional tandem rotation detector, however, has the following problems.
As mentioned above, the conventional tandem rotation detector can detect both the rotation angles of the rotary shafts 104A and 104B to detect a rotation angle difference between both rotary shafts. In this case, since any amount of magnetic flux 109A leaks out of the first rotation angle detection mechanism 102A toward the second rotation angle detection mechanism 102B as shown by an arrow, it might affect the performance of detection of the rotation angle of the rotary shaft 104B. Likewise, since the magnetic flux also leaks out of the second rotation angle detection mechanism 102B toward the first rotation angle detection mechanism 102A, it might also affect the performance of detection of the rotation angle of the rotary shaft 104A. To prevent the influence of such a leakage flux, a shielding plate can be provided between the first rotation angle detection mechanism 102A and the second rotation angle detection mechanism 102B, but only the shielding plate is not enough to prevent the influence of the leakage flux. Even in this case, the leakage flux still affects the performance of detecting the rotation angles.